The long-term goal of this study is to establish the molecular mechanism underlying the regulation of the homeostasis system. The overall blood coagulation potential dramatically increases with aging. This may have a great clinical significance in the increased frequency of thrombotic and cardiovascular disorders with advancing age. As a first model gene for us to gain insights into the underlying mechanism, we have analyzed the relationship of the structure and age-associated regulation of the factor IX gene with transgenic mice. We have successfully identified a small 5' upstream region (about 400 bp) of the gene to be critical not only for its age-associated regulation, but also for its tight liver specific expression. This region is a part of the Line 1 repetitive sequence, thus identifying the novel biological functions for the repetitive sequence.